FIGURE 1.
Robber flies are among the few insects that catch their prey in mid-flight.
They seize their prey in flight and inject their victims with saliva
containing neurotoxic and proteolytic enzymes.

FIGURE 2.
The head of an adult robber fly has a depression between the eyes when
viewed from the front.

FIGURE 3.
Robber flies have long, strong legs for grabbing prey.

FIGURE 4.
Robber flies have leg that are armed with spines and hooks to aid in prey
capture.

Yes
(mounted specimen for viewing available in insect collection at County Extension
Office)

One hot and humid morning, a gardener works busily at
weeding his azalea bed. He looks up to wipe the sweat from his face and sees
a dark, skinny fly perched on an azalea stem. The gardener thinks about the
lunch he plans to eat on his shaded patio in a few hours.

Just about the time he decides to swat the fly to keep it
off his lunch, the fly swoops off its perch, grabs a grasshopper in midair
and carries it back to his perch. The little hunter proceeds to eat a late
breakfast and the gardener proceeds to reconsider his plan to kill the fly.

And well he should. This fly is a member of the family
Asilidae, better known as robber flies. Robber flies and their larvae are
voracious predators of a wide variety of pests: beetles, wasps,
grasshoppers, leafhoppers, wasps and others. The family is an abundant one,
with nearly 1,000 species in North America, 250 of which live in Texas.

Asilids are also a diverse family, which can make them
hard to identify. The most commonly seen species have gray or black bodies.
However, some are orange and some are black and yellow, mimicking their
prey, the bumblebee. Worldwide, they range in size from 3 mm to 50 mm (about
2 inches)!
They are true flies (Order: Diptera, having two wings). The characteristic
that distinguishes them from other flies is a hollow space between their two
large eyes.

Most family members have a long, narrow, tapering abdomen
containing segments. They are “bearded,” having fine hair that covers their
piercing mouthparts. The six legs are usually long, bristled, and strong for
grabbing and holding prey. Adult are active in the warm summer months and
they like sunny, arid hunting grounds the best.

The life cycle of the robber fly is a complete
metamorphosis. An adult female lays whitish eggs in a mass that she then
covers with a chalky protective covering. Eggs can be found on low plants,
grasses or in crevices within soil, bark or wood.

Robber fly larvae are seldom seen, even though they can
grow to 1¼ inches long. They resemble long, slender, light-colored worms
with knobby projections on the six center segments of their bodies. Living
in the soil or decaying wood, this immature stage consumes organic matter,
white grubs, beetle pupae, grasshopper egg masses and other soft-bodied
organisms.

Robber flies overwinter as larvae and pupate in the soil.
As the weather warms up, the puparia migrate to the surface and emerge as
adults. The entire life cycle takes at least a year.

Robber flies are among the few insects that catch their
prey in mid-flight. An individual establishes a perch zone. From there, it
swoops out to snatch the unsuspecting victim that is often larger than its
aggressor and may even include spiders, large predatory insects, and,
sometimes, other robber flies.

After injecting the hapless meal with saliva that
paralyzes and digests the prey’s bodily contents, the robber fly retires
back to its perch and slurps up its insect smoothie. Although humans are
never on its menu, a robber fly can inflict a painful bite if mishandled.

Robber flies are not picky. The down side to their
eclectic appetites is that they will dine indiscriminately on those insects
we gardeners consider beneficial. The upside is that they eat harmful pests
just as enthusiastically. Overall, robber flies are considered to play an
important role in maintaining a healthy balance in our gardens.